Unveiling the role of stratified extracellular polymeric substances in membrane-based microalgae harvesting: Thermodynamic and computational insights

Wenxin Song; Jiaying Ma; Shiyong Miao; Qipeng Zhao; Huaqiang Chu; Xuefei Zhou; Yalei Zhang

doi:10.1016/j.watres.2024.123079

Unveiling the role of stratified extracellular polymeric substances in membrane-based microalgae harvesting: Thermodynamic and computational insights

Water Res. 2024 Dec 31:273:123079. doi: 10.1016/j.watres.2024.123079. Online ahead of print.

Authors

Wenxin Song¹, Jiaying Ma¹, Shiyong Miao¹, Qipeng Zhao¹, Huaqiang Chu², Xuefei Zhou³, Yalei Zhang³

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China.
² State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai, 200092, PR China. Electronic address: chuhuaqiang@tongji.edu.cn.
³ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai, 200092, PR China.

PMID: 39756225
DOI: 10.1016/j.watres.2024.123079

Abstract

Membrane separation technology has emerged as a highly energy-efficient method for microalgae enrichment and harvesting in wastewater treatment. However, membrane fouling caused by algal cells and stratified extracellular polymeric substances (EPS) remains a critical barrier to its industrial-scale application. This study meticulously investigates the micro process of algae-derived pollutants stacking to the membrane surface affected by stratified EPS. The fouling process resulting from algal cell particle deposition and cake layer formation are clearly simulated using a semi-coupled computational method of Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) for the first time. The results reveal that the hydrophilic component and spatial network structure of soluble EPS (S-EPS) effectively impede the algae-membrane adhesion, and enable the algal cake layer exhibit "dynamic membrane" characteristic to enhance the organic matter retention. In contrast, bound EPS (B-EPS) with higher protein content exhibits a stronger fouling potential and adhesion tendency of algal cells. The influence of stratified EPS on the variation of thermodynamic interaction with contact scale in the sphere-plane/sphere-sphere model is inventively conducted. Based on different algal cell filtration modes, a sequential increase in the eigenvalue n was observed by delaminating EPS layer by layer, indicative of a more severe membrane pore blockage. The semi-coupled CFD-DEM method provides a quantitative analysis of the deposition process, offering spatial resolution and force analysis for algal-derived pollutants. Additionally, we propose a novel calculation method to reverse the deposition process based on the particle stress, providing a valuable reference for simulating membrane-based microalgae harvesting under the influence of stratified EPS.

Keywords: CFD-DEM; Extracellular polymeric substance; Fouling mechanism; Membrane fouling; Microalgae harvesting.